Combine dry ingredients. Whisk together flour, cornstarch, baking soda, and salt in small bowl. 2 ¼ cups (280 g) all purpose flour 2 teaspoons cornstarch 1 teaspoon baking soda ½ teaspoon salt
Combine butter and sugars. In a bowl of a whisk together the melted butter brown sugar and granulated sugar on medium speed until combined. ¾ cup (170 g) unsalted butter ¾ cup (153 g) packed light brown sugar ½ cup (100 g) granulated sugar
Add extracts and eggs. Add egg and egg yolk whisking to combine. Add vanilla and almond extract and mix just until combined. 1 large egg 1 large egg yolk 2 teaspoons vanilla extract ½ teaspoon almond extract
Add dry ingredients. Gradually stir in flour mixture, chocolate chips and rainbow sprinkles with a wooden spoon or spatula until just combined. ½ cup rainbow sprinkles 1 cup (170 g) white chocolate chips
Scoop and chill the cookies. Using a small cookie scoop, scoop each portion of the dough (heaping 2 tablespoons, about 50 g) and roll into balls. Place onto a baking sheet lined with parchment paper. Cover with plastic wrap and refrigerate for at least 2 hours (ideally overnight).
Prep oven and pan. Position a rack in the center of the oven. Preheat the oven to 350°F (180℃). Like baking sheets with parchment paper.
Bake and cool cookies. Bake the cookie sheet on the middle rack for 10-12 minutes, until edges are set and centers are slightly puffed. Remove from the oven and let cool on a baking sheet for 5 minutes before transferring to a wire rack to cool completely. When the cookies come out I like to place on top a few extra chocolate chips for appearance and use a round cookie cutter on the outside edges and rotate around to make the cookies perfectly circular.